VIENNA —
The implementation of a landmark nuclear agreement between Iran and six world powers is expected to begin in late December or early January, Tehran's envoy to the U.N. atomic agency said on Friday.

Under the November 24 interim accord, Iran will curb its nuclear program in exchange for limited sanctions relief, seen as a first step towards resolving a decade-old dispute that has stirred fears of a new Middle East war.

Asked when the six-month period covered by the agreement would start, Ambassador Reza Najafi told reporters: “We expect that either the end of December or beginning of January we should start implementing the measures agreed by both sides.”

The deal between Iran and the United States, France, Germany, Britain, China and Russia is designed to halt any further advances in Iran's nuclear campaign and to buy time for negotiations on a final settlement.

After years of confrontation, it has underlined a thaw in relations between Iran and the West after the election in June of a relative moderate, Hassan Rouhani, as Iranian president on a pledge to end Tehran's isolation and win relief from sanctions that have battered the oil producer's economy.

Iran agreed under last Sunday's half-year accord to stop its most sensitive nuclear work - uranium enrichment to a fissile concentration of 20 percent - and cap other parts of its activity in exchange for some relief from sanctions, including on trade in petrochemicals and gold.

Refined uranium can fuel nuclear power plants but also the fissile core of a bomb if processed to a high degree.

The Islamic Republic says the nuclear program is a peaceful energy project but the United States and its allies suspect it has been aimed at developing the capability to produce nuclear weapons.

More work for UN inspectors

Western diplomats said sanctions relief should enter into force all at once, at an implementation date which is yet to be decided. That date will depend on verification by the U.N. nuclear agency that Iran is fulfilling its end of the bargain.

Some said they expected Iran to halt its 20 percent enrichment earlier than the implementation date, but that it needed time for other undertakings such as the conversion and dilution of its stockpile of that higher-refined material.

No new sanctions on Iran would be introduced while the details of the implementation were being worked out, they said.

Asked when Iran would stop its higher-grade enrichment, Najafi said: “We need first to have a meeting for coordination and as soon as we agree on a date we will start implementing the measures agreed by Iran.”

A Western diplomat earlier this week gave a somewhat less ambitious timetable, saying implementation of the agreement was expected to get under way towards the end of January.

“Now we move into the extremely complex and difficult implementation phase,” the envoy added.

Western officials and experts caution that finding a permanent solution to the dispute will probably be an uphill struggle, with the two sides still far apart on the final scope and capacity of the Iranian nuclear program.

Najafi said Iran had already held preliminary discussions with the U.N. nuclear agency, which will expand its monitoring in the country to ensure that it is honoring the terms of the accord, and that those would continue.

The head of the International Atomic Energy Agency, Yukiya Amano, said on Thursday that the IAEA would probably need more money to help it carry out its increased workload in inspecting Iranian uranium enrichment plants and other sites. Amano also said the IAEA would need time to prepare for the task.

Najafi said the IAEA “needs some time and of course resources should be allocated to the agency.”